1. Field of the Invention
The present invention relates to an image reading device, an image forming apparatus, and an image reading method.
2. Description of the Related Art
There is known an image reading device that detects the size of an original by pre-scanning an original area (a readable area) prior to reading of the original. Furthermore, when the image reading device reads the original, the image reading device performs a shading correction in which a white reference board is read to correct uneven illuminance, etc. of a light source thereby normalizing read original data. In the detection of the original size, a shading correction as rigorous as in the reading of the original is not required. Accordingly, to speed up the detection of the original size, there is known such a way that a shading correction is performed using previously-acquired and retained read white reference board data without reading of a white reference board.
Furthermore, due to increasing demands for power saving in recent years, there are becoming more common image reading devices equipped with an energy-saving mode function of turning off a portion of the power to an image reading device to put the image reading device into a standby state when a user does not use the image reading device for a long time. And, there are desired image reading devices capable of fast recovery from energy-saving mode.
Japanese Laid-open Patent Publication No. 2013-065973 has disclosed an image reading device that executes a shading correction using already-acquired correction data which has been stored in a correction-data storage unit in original-size detecting operation and executes a shading correction using new correction data which has been newly acquired in image reading operation.
However, such conventional technologies have a problem that the memory capacity required for original-size detecting operation is large, so it takes a long time to read data from a memory.
In view of the above-described conventional problem, there is a need provide an image reading device, image forming apparatus, and image reading method capable of improving the accuracy of detecting the original size while decreasing the storage capacity required for detection of the original size thereby reducing the readout time.